This invention relates to electronic distance measuring equipment, and, more particularly, to a compact, light weight laser range finder utilizing a semiconductor laser preferably operating in the visible light range.
A variety of technologies are available for remotely determining the distance from a source to an object. Generally, these approaches involve emitting some type of energy toward the object and receiving a portion of the energy reflected back from the object or a reflective target (such as a corner-curb prism) placed at the object. The distance from the source to the object is determined by one of several approaches.
Three types of energy are in widespread use for distance measurement. Radio frequency signals are used to measure long distances where the desired radiation pattern from the emitter is broad, radar being an example. Ultrasonic signals are used to measure shorter distances where the desired radiation pattern from the emitter is broad, sonar being an example.
Where the distance to a well-defined object is to be measured, the use of a light beam is preferred. The light beam is emitted from a source, travels to the object or reflective target, is reflected from the object or reflective target, and returns to the emitting instrument. The light beam may be precisely defined, and the measurements are less subject to multipath interference and adverse environmental effects than are other techniques. Several different measurement approaches are available to determine distances using a light beam, including time of flight, phase difference, and code correlation techniques. For some applications, the light may be non-coherent light such as produced by light emitting diodes, and for others the light is coherent light such as produced by a laser. A variety of light-beam-based measurement instruments are available commercially, using these various techniques and light sources.
The available devices for measuring distances using the propagation of a beam of light which employ light in visible wavelengths typically are large in size, are not rugged, and require the use of a reflective target even at relatively short distances (i.e., less than a few feet) or use light sources that are too powerful for safe general applicability. By contrast, the available devices which employ light in non-visible (usually infrared) wavelengths typically use light-emitting diodes and are smaller and rugged, but suffer from the drawback that the light beam cannot be seen with the human eye. These limitations are important in the practical utilization of the distance measuring equipment. When the light used to measure distances is not visible, the user cannot be certain that the beam is reflecting from the intended surface so that the spatial resolution of the object is limited. Large, fragile gas-based lasers used in visible-light distance measuring equipment cannot be used in many applications that require the measurement device to be easily carried and moved.
As indicated, many ranging devices usually require a reflective target placed at the object to be measured to ensure that the reflected beam will have a sufficiently large amplitude for measurement and analysis. In some instances a separate reflective target may be easily provided, but in other practical applications the need for a reflective target placed at the object is a substantial detriment. For example, if a surveyor wishes to measure the height of a tower, it is highly inconvenient, and sometimes impossible, to place a reflective ranging target at the top of the tower. Conventional triangulation procedures must instead be followed.
To avoid the need for a reflective target, in some cases the power of the light source may be increased to increase the amplitude of the returned signal. This response has the limitation that the beam may become dangerous to the vision of unprotected eyes and to the skin. A high-power light source also consumes a large amount of energy, preventing it from being readily portable by a single person.
There is a need for a light-based ranging device, that preferably operates in the visible light range so that the object can be readily discerned, has excellent spatial resolution at the object, is accurate in the measured distance, requires no reflective target up to intermediate distances, is portable and rugged, has a low power requirement, and is not unduly dangerous to the operator or other person who may momentarily view the beam. The present invention fulfills this need, and further provides related advantages.